1. Field of the Invention
The invention relates to an image resolution conversion technique and more particularly to an image resolution conversion method performed in a scaling phase and a smoothing phase.
2. Description of the Related Art
This application claims the benefit of Taiwan Application No. 97125041 entitled “IMAGE RESOLUTION ADJUSTING DEVICES, DISPLAY DEVICES AND IMAGE RESOLUTION ADJUSTING METHODS” filed on Jul. 3, 2008. The disclosure of the Taiwan Application is incorporated herein.
For current display devices, electronic monitor systems are widely applied in various applications, such as digital cameras, liquid crystal display (LCD) devices, and LCD televisions. In order to conform to specifications of electronic monitor systems with different resolutions, the resolutions of image sources have to be controlled by scaling images. For example, when a resolution of an input image is in VGA mode (640×480) while an output device is in XGA mode (1024×768), the resolution of the input image has to be enhanced, and when a resolution of an input image is in SXGA mode (1280×1024) while an output device is in XGA mode (1024×768), the resolution of the input image is degraded.
Conventional image scaling control techniques usually use resolution (i.e. pixel or line of an image) interpolation or replication during an image upscaling period. An image which is upscaled by interpolation advantageously has smooth edges from the perspective of human vision; however, the content of the original image is changed so as to result in image degration for its accuracy. When an image is upscaled by replication, disadvantageously, the image has sawtooth edges if the scaling ratio for the image is not controlled appropriately, resulting in degraded quality of the image.
Please referred to FIG. 1, U.S. Pat. No. 6,587,602 discloses a resolution conversion method. It is a process for converting an original digital image into another digital image having a different number of pixels. In this prior art, the original image is converted into an enlarged image by generating pixels to be interpolated to increase the number of pixels. Besides, a function f1 links the gray scale levels of adjacent pixels so as to generate interpolation pixels such that the gray scale levels thereof are positioned on the function f1. On the other hand, if the difference between the gray scale levels of the adjacent pixels is greater than the predetermined difference threshold, a function f2 links the gray scale levels of adjacent pixels so as to generate interpolation pixels such that the gray scale levels thereof are positioned on the function f2. However, the prior art uses interpolation to provide the resolution conversion so as to cause original pixel data change from the source image unfortunately, and it is not appropriate in some cases of the emergent medical surgery because this situation does not allow any change of original pixel data to prevent any of the medical mistakes from viewing the original medical images.
Besides, U.S. Pat. No. 7,199,837 also discloses a system for improving a ratiometric expansion. The prior art provides, after an image being enlarged by a replicator, the resolution of the image re-adjusted by a re-sampler. However, the prior art is trouble with disadvantageously complicating image scaling calculation and smoothness.